1 INTRODUCTION

Occurrence of various cracks patterns in the building during construction, and after completion when it is subjected to super imposed load or during the service life, is a common phenomena’s. A building component develops cracks whenever the stress in the component exceeds it’s strength. Stress in the building component could be caused by externally applied forces, such as dead, live, wind and seismic loads, foundation settlement e.t.c or it could be induced internally due to thermal movement, moisture changes elastic deformation, chemical reaction e.t.c

Cracks in building could be broadly classified into two, as structural and non-structural cracks.

Structural Cracks: These occur due to incorrect design, faulty construction or overloading and these may endanger the safety of the building eg extensive cracking of an RCC beam (rein force concrete course)

Non-Structural Cracks: These are mostly due to internally induced stresses in building but may look unsightly, or may create an impression of faulty work or may give a feeling of instability in some situation due to penetration of moisture through them, non-structural cracks may spoil the internal finishes thus adding to the cost of maintenance, or corrode the reinforcement, thereby adversely affecting the stability of the structure in long run e.g vertical crack in a long compound wall due to shrinkage or thermal movement.

Cracks may appreciably vary in width from thin hair crack barely visible to naked eye to gaping crack. Depending upon the crack width crack are classified as.

(a) Thin Crack — less than 1 mm in width

(b) Medium Crack — 1 to 2mm in width

(c) Wide Crack — more than 2mm in width

(d) Crazing — Occurrence of closely fine cracks at the surface of a material these is called crazing.

Cracks may be of uniform width through out or may be narrow at one end gradually widening at the other end. Cracks may be straight, toothed, stepped, map pattern or random type and may be vertical, horizontal or diagonal.

Cracks may be only surface and extend to more than one layer of materials. Cracks due to different causes have varying characteristics and by the careful observations of these characteristics, one can diagnose the causes of cracking for adopting the appropriate reduced measures. Small magnitude causing tension and shear stresses can lead to cracking. Internal stress are induced in the building component on account of thermal movements, moisture change, elastic deformation, chemical reaction etc.

All these phenomenon causes dimensional changes in the building components, and whenever this movement is restraint due to interconnectivity of various member, resistance between the different layers of the components etc. stresses are induced and whenever these stresses (tensile or shear) exceed the strength of material cracks occurs.

Depending upon the cause and certain physical properties of building materials, these cracks may be wide, but further apart or may be thin but more closely space. As a general rule, thin cracks even though closely spaced and greater in number, are 1ess damaging to the structures and are not so objectionable from aesthetic to the structure and other consideration as fewer number of wider cracks.

 

2.0 STATEMENT OF THE PROBLEM

The statement of the problem can as well be the causes of crack in building. Which are as stated below

For the structural cracks

• Incorrect design

• Faulty construction

• Overloading

Cracking of an RCC beam which can lead to extensive cracking of RCC beam which may endanger the building safety.

Non-structural cracks involved

• Moisture change

• Thermal movement

• Elastic deformation

• Creep

• Chemical reaction

• Foundation movement and settlement of soil

• Growth of vegetation

Those element are mostly due to internally induced stresses in building materials and do not endanger safety of a building but may look unsightly, or may create an impression of faulty work or may give a feeling of instability in some situation due to penetration of moisture through them. Non-structural cracks may spoil the internal finishes thus adding to the cost of maintenance, or corrode the reinforcement thereby adversely affecting the stability of the structure in the long run e.g vertical crack in a long compound wall due to shrinkage or thermal movement.